Hello, I also own a WL700gE, and I also consider use WL700gE as AP if I find a suitable router (to release CPU resource of wl700gE for NAS).
I find the answer (
http://vip.asus.com/forum/view.aspx?...Language=zh-tw) of your problem at ASUS forum@Taiwan (I am a Taiwanese). Here is my translation, I try my best :-)
In brief, "When you set WL700gE in AP mode, you must "power down WL700gE and Unplug AC power line, then reconnect Power line and reboot".
Note, I have not test it yet, but according to the answer from the forum, after reboot, AP mode should work fine and the WAN port become LAN port (i.e. you got 5 LAN port at AP mode).